A communications system may be used to connect together components of a power converter, such as an AC to DC converter or a DC to AC inverter. The converter may be for applications ranging from low voltage chips, to computers, locomotives and high voltage transmission lines. More specific example applications are for switching in high voltage dc transmission lines of the type which may, for example, carry power from an offshore wind installation, and medium voltage (for example greater than 1 KV) switching for motors and the like, for example locomotive motors.
The components of the converter connected by the communications system might be controllers such as intelligent devices which determine the required state of a collection of power switching devices, switching units such as intelligent “gate drives” which control the state of an individual power-switching device such as an insulated gate bipolar transistor (IGBT), sensors such as temperature or current sensor, or actuators such as a cooling system pump. Examples of such power switching devices include IGBTs as mentioned above, alternatively however may be FETs such as MOSFETS (vertical or lateral) and JFETs, or potentially devices such as LILETs (lateral inversion layer emitter transistors), SCRs and the like. The techniques we will describe are however not limited to any particular type of general converter architecture or any particular type of power switching device.
Considering specifically communication between a controlling device (CD) and one or more power switching units (SU) of a power electronics system, there is generally a control channel conveying switching information, and a data channel conveying configuration information. In power electronics, voltage isolation is generally required between a CD and SU. Thus, physical communications links may be provided either by optical means (opto-couplers or fibre transceivers), electrical means (inductive or capacitive coupling) or RF means.
For example, a power-electronics systems may comprise a point-t)-point fibre-optic pair between a controller and a switching unit—referred to as a legacy fibre-optic network (LFON). In this scheme one fibre carries control data from the controller to the switching device where “light on” means “turn on”; the other fibre carries fault data from the switching device to the controller where “light off” means “fault”. Any further information has to be transmitted by an alternate communication channel, e.g., such that the control/fault and data streams are carried on physically separate channels (wires). However, the cost of any additional physical link is high, both in terms of board area and component cost.
Therefore, there remains a need for an improved communications method or system, preferably having advantages such as, inter alia, reliable switching operation of each power switching device, high efficiency and/or low power dissipation of the power converter (for example reducing power consumption associated with switching of power switching devices), known latency, low skew, reduced cost of manufacturing, reduced size, and/or backwards compatibility with existing system components (e.g., components designed for LFON), etc.